An unusually high frequency of post transfusion (PTH) among recipients of hepatitis B surface antigen (HBsAg) positive and negative commercial blood units at this hospital led to the development of chronic hepatitis in a large segment of our blood recipients. Three years ago a prospective study was undertaken with the objectives of following these unique, well characterized patients with post transfusion chronic liver disease to determine the risks, if any, of simultaneous transfusion of HBsAg and its antibody (anti-HBs), to characterize the natural course of the chronic sequelae of acute hepatitis and to determine if chronic liver disease is more frequently a sequelae of HBsAg positive hepatitis or of non B PTH. Data obtained in the first three years of this study suggest that the histologic appearance of unresolved hepatitis (UH) may revert on follow-up to the picture of chronic persistent hepatitis (CPH), that the risk of CH after HBsAg positive blood may be no greater than the risk after HBsAg negative blood if PTH develops and that the simultaneous transfusion of anti-HBs and HBsAg does not provide an added risk. It is proposed that the long term follow-up of these patient groups be extended to characterize the histologic, biochemical and clinical differentiation of the sequelae of non A non B acute hepatitis and to determine at what frequency spontaneous reversion from one histologic, biochemical or clinical picture to another occurs. It is equally important to assess the natural course of chronic hepatitis after PTH and to determine the risks associated with non A non B PTH as compared with hepatitis B. We therefore propose to prospectively follow those patients with CH already identified and to assess the clinical, biochemical and histological progression of disease. New patients will be similarly followed in order to adequately document the alterations within each of these unique patient populations.